How scientists can safely put antifreeze in your frozen yogurt

You want your food to be really cold, but not frozen - unfortunately, chemical antifreeze kills people. Find out how biological antifreeze is formed, and how companies are going to use it.

Traditional antifreeze can't go in food products. It's not that it's unpalatable. In fact, it's so sweet that there are products used in manufacturing specifically designed to ruin the taste of antifreeze so that people don't drink it. The problem is that chemical antifreeze kills people, and the FDA frowns upon that. Biological antifreeze, on the other hand, has been around for a long time. Fish, insects, and bacteria in cold climates have antifreeze proteins (AFPs) in their bodies which keep their fluids from turning to ice.

The AFPs in a living organism have to solve a tricky problem. Although they must bind to ice crystals immediately, before the ice spread and freezes the area around it, AFPs cannot bind to liquid water. If they do, they'll dry the organism from the inside out. Ice and water are made from the same recipe - they're both two hydrogen atoms and an oxygen atom - so the proteins have to distinguish water from ice using something other than their atomic makeup.

Studies done of the AFPs of arctic fish found that antifreeze proteins masquerade as ice in order to trap it. Although AFPs don't bind to water in the animal, they do make use of it. AFPs are made up of hydrophilic amino acids, which hold on to water, and hydrophobic ones which repel water. Their hydrophilic sites grab onto water molecules and form them into a cage. Six rings, each made up of several water molecules, are linked together by the hydrophilic parts of the AFP. The gaps between the water molecules fill with the hydrophobic parts of the AFP. These repel water molecules, but will hold on to ice. So the AFPs patrol the body of arctic animals, caging up any tiny ice crystals before they do any damage, while leaving liquid water alone.

Antifreeze proteins are a must in the food industry, especially in products such as low-fat ice creams and frozen yogurts. Generally, these products replace fat with water, which freezes solid in cold temperatures. Mixing in antifreeze proteins with the ice cream keep these foods from turning into large blocks of ice. AFPs aren't confined to the frozen food section, though. Plenty of plants use them to get through cold winters, and finding a way to get them into more delicate plants could make crops resistant to frosts. Medicine can also use AFPs in cryogenic procedures, to keep ice from damaging delicate tissue.

Via Online Library and Queen's University.